There are numerous sign cabinets in the prior art, many consisting of aluminum extruded frames. However, most of the prior art cabinets are directed to securing one or more translucent rigid plastic sign faces.
For example, Davies, U.S. Pat. No. 3,835,613 shows a frame with retainers 4 and 5 adapted to hold a rigid plastic display face 7 in an offset 50 (see FIGS. 4 and 5). The panel 7 has a shoulder which rests upon the offset 40.
Brooks, U.S. Pat. No. 4,007,552 likewise shows an extruded aluminum web 18A to secure a rigid sign face 12 against the main frame 14. Sign face 12 has shoulders 82 which are secured upon offset 26 of the main frame.
Lloyd U.S. Pat. No. 3,391,481 shows aluminum retainers such as 6 in FIG. 5 extending along the sides of the frame. A rigid panel B is held in place by the retainer and seats on all four walls formed by the retainer 6.
Angier U.S. Pat. No. 3,390,259 shows an aluminum frame forming central enclosures at 22 and 38 to house flourescent tubes, etc. and a skirt extending from each side, one end of the skirt forming a drainage channel and the opposite end seating rigid panels 2 and 4. The panels are supported at the bottom by retainer 56.
Brooks U.S. Pat. No. 3,235,989 discloses a main frame 2 with retainers 39 forming walls 53 and 54 to form a flange which holds rigid panels 22 in the flanges which extend along the bottom of the frame.
Some of the prior art shows means to tension a display face in the form of a film. For example Braun U.S. Pat. No. 3,722,119 discloses a polyvinyl chloride film 41 held and sealed from the elements by a pane 36, strips 38 and flaps 40 within a frame designated 24. Dow U.S. Pat. No. 2,573,318 shows a fabric banner 3 mounted under tension by rotatable clips 7.
Other prior art teachings are related to tensioning fabrics suitable for screen printing. For example Knowles U.S. Pat. No. 2,893,162 shows an arcuate clamp 17 extending along the entire length of each side of the frame. The clamp contains a pair of bars 20 and 19 which engage the marginal edges of the screen and secure it in the arcuate portion of the clamp 17. Tension is placed upon the screen by adjusting the nut 21.
Likewise Alter U.S. Pat. No. 4,041,861 is directed to a clamping means for screen printing. In this disclosure a clamp 24 is slidable on a rail 27 which is integral with a bar 23. The bar is moved into tensioning position by means of bolts 14. In this disclosure, the clamps secure substantially the entire marginal edge of screen 11, the clamps at each corner of the frame being slidable along the rail (such as at end E in FIG. 2) after full tension force is attained.
One of the basic problems with prior art sign cabinets is that they are directed to securing rigid plastic sign faces. These devices are not designed to provide sufficient structural strength to maintain a flexible PVC sign face under the substantial tension required to withstand forces exerted by wind gusts exceeding 100 miles (160 kmh) per hour. Wind velocities of this nature are common and often exceeded in many parts of the United States. Prior art rigid plastic faces tend to "blow out" at wind velocities of 100 miles per hour (160 kmh) or less and further are highly susceptible to vandalism, such as throwing objects at a sign face. In contrast, PVC sign faces suspended under tension will withstand wind velocities exceeding 100 miles per hour (160 kmh) without breaking and are also highly resistant to impacts such as from thown rocks which tend to bounce off the tensioned face. Further, PVC sign faces resist propagation of cuts or holes even when the cuts are not repaired. PVC sign faces thus offer a great many advantages over prior art rigid translucent plastic faces.
The few prior art devices that are designed to clamp and secure flexible sheets under tension are generally patterned after the sign cabinets used to house rigid plastic faces. Sign cabinets of this kind are not satisfactory to suspend flexible faces as it has been found that large PVC sign faces supported under tension and exposed to significant wind gusts exert extreme forces on the perimeter of the cabinet. Such forces are the result of the force on the frame produced by mounting the face under tension as well as the force of the wind exerted against the sign face. In order to compensate for these forces and to prevent buckling of the frame, it is necessary in prior art cabinets to add a considerable number of support or cross braces. This results in added weight and expense in relation to both production of the frame and installation at site.
Additionally, prior art cabinets, such as those disclosed by Braun and Dow, secure the marginal edges by panes or rotative clips. Using these prior art devices, it is difficult to suspend a flexible sign face of large size without attendant wrinkling and puckering which result in uneven appearing faces.
This invention alleviates the above problems by providing a box beam coextensive with the sign cabinet frame. The box beam when viewed in cross-section has a rectangular configuration and supports a clamping system along one side which maintains the PVC sign face under proper tension. The beam adds considerable strength to the cabinet and therefore the length of span between support members is greatly increased, thus decreasing the need for complex support braces and the weight of the cabinet.